Block copolymers may be used in directed self-assembly processes to form patterns without requiring a photolithographic process. The block copolymers can form the patterns by assembling on a neutral or patterned surface having neutral and polar regions. Such a neutral or patterned surface can be afforded by use of a polymer brush underlayer.
Polymer brushes are polymeric chains affixed to a surface of a substrate formed of, for example, a semiconductor material. The surface is reactively modified to the desired thickness and surface energy using polymer brush precursors with a desired composition. The composition of a random copolymer brush layer is tuned to afford the desired neutral surface. For block copolymers capable of self assembly but for which it is unfeasible to synthesize random copolymers of repeating units of each block (such as where different polymerization mechanisms would be required, or where the composition of the brush copolymer is not), end-group functionalization or incorporation of reactive-group containing monomers in the brush copolymer has been performed. (See, e.g., P. Mansky, Y. Liu, E. Huang, T. P. Russell, C. Hawker, “Controlling polymer surface interaction with random copolymer brushes”, Science, 275, 1458, (1997)).
Such compositional modifications to the brush copolymer are designed to provide functional sites for grafting. However, there is no disclosure in the art of adjusting the brush polymer composition to change surface polarity lithographically, and hence form a patterned surface on which the self-assembling layer can form.